Semiconductor laser element and laser device using the same element

ABSTRACT

A semiconductor laser of this invention, having a structure of an element composed of: carrier block layers, formed bilaterally externally of an active layer in section which is formed in the vertical direction from the surface of the element, for reducing a light guiding function of the active layer; wave guide layers provided bilaterally externally of said carrier block layers and clad layers provided so that the wave guide layers are sandwiched in between the clad layers. This invention overcomes a dilemma inherent in the conventional weakly guiding laser and LOC structured laser in terms of designing the device for controlling a guided mode. The present invention also solves the problems in terms of attaining higher outputting and a low dispersion of the radiation beams and improving a beam profile.

This application is a continuation-in-part of applicants' parentapplication Ser. No. 08/129,147 filed Oct. 5, 1993, now abandoned, whichparent application is incorporated herein in its entirety by referencethereto.

TECHNICAL FIELD

The present invention relates generally to industrial fields in whichhigh-output semiconductor lasers are employed for communications,optical recording on optical disks or the like, laser printers, lasermedical treatments, laser machining, etc. The present invention relates,more particularly, to a high-output semiconductor laser for asolid-state laser excitation requiring laser beams having an enhancedoutput and a small radiation angle or for a harmonic conversion elementexcitation and also to a laser device using this semiconductor laser.

BACKGROUND ARTS

It has been desired in many sectors that the output of the semiconductorlaser be enhanced. A factor for hindering the output enhancement persingle mode of the semiconductor laser is an exit surface fusion causedby the laser beam which is called catastrophic optical damage (COD). TheCOD is conspicuous especially in an AlGaAs laser. Paying attentionmainly to a reduction of a power density of the laser by expanding alaser guided mode, a weakly guiding laser having a thin active layer ora separate confinement type laser known as a large optical cavity (LOC)structure has hitherto been examined.

Based on such a structure, however, a strong correlation exists betweena refractive index and a bandgap of each mixed crystal in a variety oflaser materials ranging from the AlGaAs system. It is thereforeimpossible to independently control a carrier confinement and an opticalconfinement in a waveguide.

In particular, the expansion of the guided mode requires the thin activelayer in either the LOC structured laser or the weakly guiding laser forthe output enhancement. Further, a wide active layer is needed forobtaining a high gain for oscillations in the expanded guided mode. Aself-contradiction thus exists therein. As a matter of fact, a limit ofthe mode expansion in an epitaxial direction by the above-mentionedmethods is approximately 1 μm at the maximum. A limit of the output ison the order of 100 mW per single mode.

Besides, in the weakly guiding laser having the thin active layer, theguided mode in the laminated direction exhibits an exponential functionprofile. Hence, a radiation density in the active layer where thecatastrophic optical damage is caused is high as compared with the wholebeam intensity. This is disadvantageous for the output enhancement.Besides, the guided mode has tails drawn deeply in the clad layers, andhence there is needed a growth of the clad layers that is considerablythick for the expansion of the guided mode.

In addition, both the guided mode (near-field pattern) and a beamradiation angle (far-field pattern) deviate largely from the Gaussianbeam conceived as ideal one. There exists a problem in terms of aconvergence of the beams in multiple applications.

On the other hand, there have also been examined lasers based on aso-called window structure in which the vicinity of an exit surfacewhere a COD may occur is made transparent to the laser emission beam anda structure where a carrier injection is not effected in the vicinity ofthe exit surface. Those structures generally present, however, suchproblems that the astigmatism increases in addition to a complicatedmanufacturing process.

Further, there has been made an attempt to manufacture the high-outputlaser in the single mode by an optical feedback between a multiplicityof semiconductor lasers. The problem is, however, that the devicebecomes complicated.

It is an object of the present invention in view of the fact thatmulti-layered thin films have been easily formed by the molecular beamepitaxial (MBE) method, the metal organic chemical vapor deposition(MOCVD) method, etc. in recent years to solve the problems inherent inthe conventional weakly guiding lasers and the LOC structured lasers interms of overcoming the dilemma in designing the device for controllingthe guided mode, attaining the output enhancement, the low dispersion ofthe radiation beams and improving the beam profile.

DISCLOSURE OF THE INVENTION

According to the present invention, barrier layers (hereinafter referredto as "carrier block layers") having barrier heights and widths enoughto cancel a guiding characteristic of an active layer and perform acarrier confinement in the active layer are inserted on both sides ofthe active layer of an ordinary double hereto laser or a quantum welllaser. It is therefore possible to perform the confinement in the guidedmode and independently design an active layer thickness required foroscillations.

On this occasion, a guiding function of the active layer can becancelled by the carrier block layers by reducing the thickness of theactive layer region and the thickness of the carrier block layers to1/N^(th) (N=2 to 9) or less of the oscillation wavelength. Under suchconditions, the wave guide layers are further formed, and clad layershaving a small difference of refractive index are formed at both sidesof the wave guide layer for the purpose of controlling only lightguiding. Formed alternatively are wide wave guide layers based on agraded-index structure of a straight line, a quadratic curve, etc. It isthus possible to design the guided mode completely independently of theactive layer design parameters, thereby obtaining a stable modeapproximate to the Gaussian beams and the radiation beams having thehigh output and low dispersion angle.

With the intention of enhancing the output of the semiconductor laser byavoiding the .[.concurrent.]. .Iadd.catastrophic .Iaddend.optical damageon the exit surface and of decreasing a divergence angle of the beamradiation, it is required that the guided mode be expanded by setting toso-called weakly guiding. The optical gain in the active layer, however,has a certain limit as seen in the gain saturation of, e.g., the quantumwell laser. For this reason, the wide active layer or multi-quantum wellstructure are required for maintaining the oscillations in the expandedguided mode. This induces the self-contradiction with the weakly guidingstructure and therefore causes a problem in terms of designing a laserdiode having a high-output and a low radiation beam angle.

The number of the quantum wells and the thickness of the active layerfor giving the necessary optical gain to the oscillations can be setindependently from the wave guide structure because of the existence ofthe carrier block layers incorporating the anti-guiding functiondescribed above. Particularly, the guiding function of the active layerregion is cancelled by the anti-guiding function of the carrier blocklayers. The design of the active layer is compatible with the design ofthe guided mode by further separately introducing, into the wave guidelayer a mechanism for controlling the guided mode, as illustrated inFIGS. 1-(a), 1-(b) and 1-(c), a refractive index distribution of astepped, straight line or quadratic curve. It is therefore feasible toobtain the stable wave guide mode approximate to the Gaussian beamshaving the high-output, and low beam divergence.

The present invention can be readily actualized by use of the thin filmsemiconductor manufacturing equipment such as a molecular beam epitaxial(MBE) system, a metal organic chemical vapor deposition (MOCVD) systemor a metal organic molecular beam epitaxial (MOMBE) system. Further, theeffects of this invention are remarkable in the laser diode using AlGaAsalloy. Substantially the same effects can be, however, expected in avariety of III-V group semiconductor materials of a GaInAs system, anAlGaInAs system, a GaInAs system and a AlGaInP system and further invarious types of II-VI group semiconductor lasers.

As illustrated in FIG. 1, the carrier block layers are interposed onboth sides of the active layer of the laser based on the conventionaldouble hereto type structure of a multiple quantum well structure. Thecarrier block layers are composed of materials having a barrier heighthigh enough to effect a carrier confinement in the active layer, i.e., asmaller refractive index and a wider gap than that of the wave guidelayer. The carrier block layers also incorporate the function to cancelthe guiding characteristic of the active layer, the anti-guidingfunction and the carrier block function.

Further, it is possible to reduce a resistance due to the formation of aSchottky barrier on a band discontinuous surface and perform effectivecarrier blocking by performing P-doping on the order of 10¹⁸ /cm³ on theP-side of the carrier block layer and N-doping on the N-side, as shownin FIG. 2.

The cancellation of the guiding function of the active layer region bythe carrier block layers having the anti-guiding function can besubstantially attained when establishing the following relationshipunder such condition that a thickness of both is 1/N^(th) (N=2 to 9) orless of the oscillation wavelength:

    d.sub.0 ·(N.sub.1.sup.2 -N.sub.0.sup.2).sup.0.5 =2·d.sub.1 (N.sub.0.sup.2 -N.sub.2.sup.2).sup.0.5

where, as substantially shown in FIG. 1, N₀ is the refractive index ofthe wave guide layer, N₁, d₀ are respectively the refractive index andthe thickness of the active layer, and N₂, d₁ are respectively therefractive index and the thickness of the carrier block layers. If theactive layer is multi-layered as seen in the multiple quantum wellstructure, a quantity corresponding to the left side is calculated withrespect to each layer. An added value may be employed for the left side.More specifically, in the case of the active layer composed of the mquantum well layers having a thickness d_(w) wherein a composition ofthe barrier layers between the quantum wells is the same as that of thewave guide layer, the guiding function of the active layer can becancelled by the .[.barrier.]. .Iadd.carrier block .Iaddend.layer whenestablishing the following relationship

    m·d.sub.w ·(N.sub.1.sup.2 -N.sub.0.sup.2).sup.0.5 =2·d.sub.1 (N.sub.0.sup.2 -N.sub.2.sup.2).sup.0.5.

When the guiding function of the active layer is cancelled by thecarrier block layers, the guided mode is independently controllable byclad layers and the wave guide layers provided therearound. It isdesirable that the wave guide is cut off with respect to a higher-ordermode for the single mode oscillations in any of the structures shown inFIGS. 1-(a), 1-(b) and 1-(c). Speaking of a step index type guidingmechanism shown in FIG. 1(a), this guided mode can be described by thenormalized frequency V. The normalized frequency V is defined by thefollowing formula:

    V=(πd/λ)·(N.sub.0.sup.2 -N.sub.3.sup.2).sup.0.5

where π is the ratio of the circumference of a circle to its diameter, λis the oscillation wavelength, d is the effective thickness of the waveguide layer including the active layer and the carrier block layer, N₀is the effective refractive index of the wave guide layer, and N₃ is therefractive index of the clad layer. If the refractive index of the waveguide layer continuously changes, the maximum value of N₀ is used.

In a symmetric waveguide, when the normalized frequency V is π/2 orunder, single mode guiding is effected. Note that guided mode exhibits aprofile of a sinusoidal function within the wave guide layer but aprofile of an exponential function within the clad layers. When V=π/2, amode confinement rate in the wave guide layer is approximately 65%.Unlike the profile of the exponential function over the substantiallyentire area of the conventional weakly guiding laser, the guided modeapproximates the Gaussian type (see FIG. 21). The structures (shown inFIGS. 2 and 3, respectively) in the embodiments 1 and 2 are designedsubstantially under this condition.

In the approximate-to-symmetry guiding structure, there is almost nopossibility in which an odd-order mode is excited. Hence, even whenmaking the mode more approximate to the Gaussian type by furtherincreasing the normalized frequency V up to a level of π, the sameeffects can be acquired without causing multiple transverse modeoscillations. The embodiment 3 having the structure shown in FIG. 4gives a design example where V is approximate to π.

More effectively, the oscillation mode can be made approximate to theGaussian type by adopting the graded-index structure as shown in FIGS.1-(b) and 1-(c).

We have repeated a trial manufacture of the semiconductor laser on thebasis of the above-mentioned as a guideline and could obtain thefollowing conditions with respect to the carrier block layer, V₀ isdefined by:

    V.sub.0 =d.sub.0 /λ(N.sub.1.sup.2 -N.sub.0.sup.2).sup.0.5

where π is the ratio of the circumference of a circle to its diameter,d₀ is the thickness of the active layer, λ is the oscillation wavelengthand N₁ is the refractive index of the active layer and N₀ is therefractive index of the wave guide layer. If the active layer consistsof .[.N-.]..Iadd.m-.Iaddend.pieces of multiple quantum wells, V₀ isexpressed such as:

    .[.V.sub.0 =N·π·d.sub.w /λ·(N.sub.1.sup.2).sup.0.5 .]. .Iadd.V.sub.0 =m·π·d.sub.w /λ·(N.sub.1.sup.2).sup.0.5 .Iaddend.

where d_(w) is the thickness of the well layer, N₁ is the refractiveindex of the well layer, and N₀ is the refractive index of the waveguide layer.

Next, V₁ is defined by:

    V.sub.1 =(π·d.sub.1 /λ)·(N.sub.0.sup.2 -N.sub.2.sup.2).sup.0.5

where π is the ratio of the circumference of a circle to its diameter,d₁ is the thickness of the carrier block layers, N₂ is the refractiveindex of the carrier block layers, and N₀ is the refractive index of thewave guide layer.

Next, V₂ is defined by:

    V.sub.2 =(πd.sub.2 /λ)·(N.sub.0.sup.2 -N.sub.3.sup.2).sup.0.5

where π is the ratio of the circumference of a circle to its diameter,d₂ is the effective thickness between the two clad layers, i.e.,effective wave guide layer thickness, N₀ is the effective refractiveindex of the wave guide layer, and N₃ is the refractive index of theclad layer.

The effective thickness between the two clad layers d₂ is defined asfollows: ##EQU1##

N_(w) ^(m) is the maximum refractive index of the wave guide layer andN_(w) (x) is the refractive index of wave guide at the position; x, x₁,x₂ are the boundary between the wave guide layer and the lower or upperclad layer, respectively. .[.The effective refractive index N₀ is amaximum value of the wave guide layer..].

As obvious from the formulas described above, V₀, V₁, V₂ respectivelycorrespond to the normalized frequencies of the active layer, thecarrier block layers and the wave guide layer. If the anti-guidingfunction of the carrier block layers is too large, a reentrant is formedin the vicinity of the active layer in the guided mode. As a result, theoptical confinement rate is decreased. This brings about an increment inthe threshold current. Accordingly, an influence of the carrier blocklayer on the guided mode has to be lessened. According to the presentinvention, a variety of trial manufactures of the semiconductor laserhas been repeated. Consequently, it was found that V₂ corresponding tothe normalized frequency of the wave guide layer is in the range ofπ/4-π.

If V₂ increases up to a level of π, multiple transverse mode is notexcited; further increasing V₂ over π may cause the second-order modeoscillation.

As V₂ decreases to far less than π/4, a guided mode profile in theactive layer becomes sharp and, it was also found that the carrier blocklayer did not disturb a trace of the whole guided mode, where thefollowing relationship is established:

    V.sub.1 <V.sub.2 /10.

Moreover, we also confirmed through the various trial manufactures ofthe semiconductor laser that especially the following condition iseffective in canceling the guiding function of the active layer by thecarrier block layer:

    V.sub.0 /3<V.sub.1 <V.sub.0.

Furthermore, the carrier block layer has to effectively confine thecarrier in the active layer. We have found out that the carrier can besufficiently effectively confined in the active layer when E>2.5·10³ /d₁², where d₁ (angstrom) is the thickness of the carrier block layer, andE (eV) is the energy gap difference between the wave guide layer and thecarrier block layer.

Herein, the composition of the wave guide layer is set preferably toAl_(x) Ga_(1-x) As (0≦x<0.35: where x is the atomic ratio) in thesemiconductor laser using Al_(x) Ga_(1-x) As.

More specifically, when Δx is the aluminum composition differencebetween the wave guide layer and the carrier block layer, therelationship between Δx and the thickness d₁ (angstrom) of the carrierblock layer preferably falls within the following range:

    Δx>(2.2·10.sup.3 /d.sub.1.sup.2), and Δx<(5.0·10.sup.4 /d.sub.1.sup.2).

Further, V₀ is given by:

    V.sub.0 =π·d.sub.0 /λ·(N.sub.1.sup.2 -N.sub.0.sup.2).sup.0.5

where d₀ is the thickness of the active layer. If the active layerconsists of N-pieces of quantum well layers, however, V₀ is defined by:

    V.sub.0 =N·πd.sub.w /λ·(N.sub.1.sup.2 -N.sub.0.sup.2).sup.0.5

where d_(w) is the thickness of the quantum well layer, N₁ is therefractive index of the quantum well layer, and N₀ is the refractiveindex of the wave guide layer. Then a relationship therebetween is setpreferably as follows:

    (V.sub.0 /3)<V.sub.1 V.sub.0.

The carrier block layers have a large bandgap on both sides of theactive layer but a small refractive index and incorporate ananti-guiding function. These carrier block layers act to reduce orcancel the guiding function incorporated into the active layer. Anotherfunction thereof is to block the injected carriers and act to confinethe electrons and holes in the active layer. This layer also undergoesP- or N-doping, thereby ameliorating the resistance reducing function orthe carrier confinement function.

The guided mode control structure of the wave guide layer and the cladlayer provides the action to control the expansion of the oscillationmode and the profile stability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a schematic sectional view of a semiconductor laser in anepitaxial direction wherein the wave guide layer contains a steppedrefractive index distribution.

FIG. 1(b) is a schematic sectional view of a semiconductor laser in anepitaxial direction wherein the wave guide layer contains a straightline refractive index distribution.

FIG. 1(c) is a schematic sectional view of a semiconductor laser in anepitaxial direction wherein the wave guide layer contains a refractiveindex distribution in the form of a quadratic curve.

FIG. 1(d) is a schematic sectional view of a semiconductor laser in anepitaxial direction showing an enlarged view of the active layer.

FIG. 1(e) is a schematic sectional view of a semiconductor laser in anepitaxial direction showing an enlarged view of a multi-quantum welllayer construction of the active layer.

FIG. 2 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 1 of this invention.

FIG. 3 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 2 of this invention.

FIG. 4 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 3 of this invention.

FIG. 5 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 4 of this invention.

FIG. 6 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 5 of this invention.

FIG. 7 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 6 of this invention.

FIG. 8 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 7 of this invention.

FIG. 9 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 8 of this invention.

FIG. 10 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 9 of this invention.

FIG. 11 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 10 of this invention.

FIG. 12 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 11 of this invention.

FIG. 13 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 12 of this invention.

FIG. 14 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 13 of this invention.

FIG. 15 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 14 of this invention.

FIG. 16 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 15 of this invention.

FIG. 17 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 16 of this invention.

FIG. 18 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 17 of this invention.

FIG. 19 is a schematic sectional view of a semiconductor laser elementaccording to an embodiment 18 of this invention.

FIG. 20 is a schematic sectional view of a semiconductor laser elementaccording to a comparative example in relation to the present invention.

FIG. 21 is a graphic chart showing guided mode characteristics in theembodiments 1-3 and a reference example.

FIG. 22 is a graphic chart showing characteristics of a radiation beamangle in the embodiments 1-3 and the reference example.

FIG. 23 is a graphic chart showing the guided mode characteristics inembodiments 4-7.

FIG. 24 is a graphic chart showing the characteristics of the radiationbeam angle in the embodiments 4-7.

FIG. 25 is a graphic chart showing the guided mode characteristics inembodiments 1 and 8-10.

FIG. 26 is a graphic chart showing the characteristics of the radiationbeam angle in the embodiments 1 and 8-10.

FIG. 27 is a graphic chart showing the guided mode characteristics inembodiments in 11-14.

FIG. 28 is a graphic chart showing the characteristics of the radiationbeam angle in embodiments 11-14.

FIG. 29 is a graphic chart showing the guided mode characteristics inembodiments 15-18.

FIG. 30 is a graphic chart showing the characteristics of the radiationbeam angle in the embodiments 15-18.

FIG. 31 is a graphic chart representing an effective range of a carrierblock.

FIG. 32 is a view illustrating a direct-connection type semiconductorlaser excitation solid-state laser device utilizing the laser elementaccording to this invention.

FIG. 33 is a view illustrating an example of a fiber connection typesemiconductor laser excitation solid-state laser device utilizing thelaser element according to this invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will hereinafter be described on the basis of thedrawings.

Epitaxial growths exhibiting profiles illustrated in FIGS. 2-20 areperformed by MOCVD growth. FIG. 2 shows an embodiment 1. FIG. 3 shows anembodiment 2. FIG. 4 shows an embodiment 3. FIG. 5 shows an embodiment4. FIG. 6 shows an embodiment 5. FIG. 7 shows an embodiment 6. FIG. 8shows an embodiment 7. FIG. 9 shows an embodiment 8. FIG. 10 shows anembodiment 9. FIG. 11 shows an embodiment 10. FIG. 12 shows anembodiment 11. FIG. 13 shows an embodiment 12. FIG. 14 shows anembodiment 13. FIG. 15 shows an embodiment 14. FIG. 16 shows anembodiment 15. FIG. 17 shows an embodiment 16. FIG. 18 shows anembodiment 17. FIG. 19 shows an embodiment 18. FIG. 20 is a schematicplan view thereof in a comparative example. FIG. 21 is a graphic chartshowing a guided mode in the embodiments 1-3 and the comparativeexample. FIG. 22 is a graphic chart showing a radiation mode in theembodiments 1-3 and the comparative example. FIG. 23 is a graphic chartshowing a guided mode in the embodiments 4-7. FIG. 24 is a graphic chartshowing a radiation mode in the embodiment 4-7. FIG. 25 is a graphicchart showing a guided mode in the embodiments 1 and 8-10. FIG. 26 is agraphic chart showing a radiation mode in the embodiments 1 and 8-10.FIG. 27 is a graphic chart showing a guided mode in the embodiments11-14. FIG. 28 is a graphic chart showing a radiation mode in theembodiments 11-14. FIG. 29 is a graphic chart showing a guided mode inthe embodiments 15-18. FIG. 30 is a graphic chart showing a radiationmode in the embodiments 15-18. FIG. 31 is a graphic chart representingan effective range of carrier block layers, wherein the axis of theabscissa indicates a difference in Al composition, and the axis ofordinate indicates a thickness of the carrier block layers.

In FIG. 31, the anti-guiding function of the carrier block layers is toolarge, and disturbs the guided mode in an upper range from the rightupper curve. Concretely, a reentrant is formed in the guided mode in thevicinity of the active layer. This brings about a decrease in theoptical confinement factor, resulting in an increment in the thresholdcurrent. Further, it follows that the guided mode deviates largely fromthe Gaussian mode, and an aberration is caused in the radiation pattern.The carrier confinement is insufficient enough to worsen a temperaturecharacteristic of the threshold current in a lower range from the leftlower curve. The guiding function of the active layer is compensatedmost optimally by the carrier block layer to exhibit the best guidedmode in a range where the following relationship is established:

    V.sub.0 /3<V.sub.1 <V.sub.0.

The embodiments falling within this range are marked with ⊚. (1)Represents the embodiment 1, and (2) indicates the embodiment 2. Thecircled numerals in the same Figure (FIG. 31) hereinafter similarlyrepresent the embodiments corresponding to the numerals.

An effective range (exhibiting the effects) in the present invention isdefined by the two solid lines.

The following is a technology common to the respective embodiment.Doping on the order of 1×10¹⁸ /cm³ is conducted by use of Se as ann-type dopant and Zn as a p-type dopant. Zinc is diffused in a stripedshape from the surface by use of an SiO₂ diffusion mask. Thereafter, atrial manufacture of a diode chip having a gain guiding structure isconducted by effecting a cleavage. After performing die-bonding to an LDmount, a light-current characteristic is measured in a pulse mode. Table1 shows characteristic of the typical chip having a stripe width of 2.5μm and a cavity length of 300 μm. Note that no optical coating isapplied to both edge surfaces.

(Embodiment 1)

As illustrated in FIG. 2, an n-type buffer layer 10 having a thicknessof 0.5 μm is formed on an n-type substrate 8 composed of GaAs. Formedsequentially on this layer are an n-type clad layer 1, an n-type lightwave guide layer 2, an n-type carrier block layer 3, an active layer4,-a p-type carrier block layer 5, a p-type light wave guide layer 6 anda p-type clad layer 7. An n-type cap layer 11 is formed as an uppermostlayer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.30 Ga₀.70 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.30 Ga₀.70 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that4-layered quantum well layers 13 are each partitioned by barrier layers14 between side barrier layers 12 deposited on inner walls of therespective carrier block layers 5, 3 in an area sandwiched in betweenp-type carrier block layer 5 and the n-type carrier block layer 3. Theconcrete configurations of this active layer 4 are given as follows:

p-type carrier block layer 5

Thickness: 165 angstrom

Composition: .[.Al₀.38 Ga₀.62 As.]. .Iadd.Al₀.50 Ga₀.50 As .Iaddend.

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.30 Ga₀.70 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.30 Ga₀.70 As

n-type carrier block layer 3

Thickness: 165 angstrom

Composition: .[.Al₀.38 Ga₀.62 As.]. .Iadd.Al₀.30 Ga₀.50 As .Iaddend.

FIG. 21 illustrates a guided mode profile (near-field patterns) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 22 shows a measured result in theradiation mode.

(Embodiment 2)

As illustrated in FIG. 3, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 2.0 μm

Composition: Al₀.31 Ga₀.69 As

p-type light wave guide layer 6

Thickness: 0.93 μm

Composition: Al₀.30 Ga₀.70 As

n-type light wave guide layer 2

Thickness: 0.93 μm

Composition: Al₀.31 Ga₀.70 As

n-type clad layer 1

Thickness: 2.0 μm

Composition: Al₀.31 Ga₀.69 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 is formed such that 8-layered quantum well layers 13are each partitioned by the barrier layers 14 as shown in exploded viewbetween side barrier layers 12 deposited on the inner walls of therespective carrier block layers 5, 3 in an area sandwiched in betweenthe p-type carrier block layer 5 and the n-type barrier layer 3. Theconcrete configurations of this active layer 4 are given as follows:

p-type carrier block layer 5

Thickness: 330 angstrom

Composition: Al₀.50 Ga₀.50 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.30 Ga₀.70 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.30 Ga₀.70 As

n-type carrier block layer 3

Thickness: 330 angstrom

Composition: .[.Al₀.30 Ga₀.70 As.]. .Iadd.Al₀.50 Ga₀.50 As .Iaddend.

FIG. 21 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 22 shows a measured result in theradiation mode.

(Embodiment 3)

As illustrated in FIG. 4, an n-type inversion layer 15 is providedbetween the p-type clad layer 7 and the p-type light wave guide layer 6.With the placement of this n-type inversion layer, the current can benarrowed down in the lateral direction in the vicinity of the activelayer 4.

Namely, the light is confined also in the lateral direction owing to then-type inversion layer 15, thereby making it possible to attain astabilized off-axial mode.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 0.8 μm

Composition: Al₀.35 Ga₀.65 As

n-type inversion layer 15

Thickness: 0.2 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.93 μm

Composition: Al₀.35 Ga₀.70 As

n-type light wave guide layer 2

Thickness: 0.93 μm

Composition: Al₀.30 Ga₀.70 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the8-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 330 angstrom

Composition: Al₀.50 Ga₀.50 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.30 Ga₀.70 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.30 Ga₀.70 As

n-type carrier block layer 3

Thickness: 330 angstrom

Composition: Al₀.50 Ga₀.50 As

FIG. 21 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 22 shows a measured result in theradiation mode.

(Embodiment 4)

As illustrated in FIG. 6, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.30 Ga₀.70 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.30 Ga₀.70 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 100 angstrom

Composition: Al₀.38 Ga₀.62 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.30 Ga₀.70 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.30 Ga₀.70 As

n-type carrier block layer 3

Thickness: 100 angstrom

Composition: Al₀.38 Ga₀.62 As

FIG. 23 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 24 shows a measured result in theradiation mode.

(Embodiment 5)

As illustrated in FIG. 6, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.30 Ga₀.70 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.35 Ga₀.70 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 200 angstrom

Composition: Al₀.38 Ga₀.62 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.30 Ga₀.70 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.30 Ga₀.70 As

n-type carrier block layer 3

Thickness: 200 angstrom

Composition: Al₀.38 Ga₀.62 As

FIG. 23 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 24 shows a measured result in theradiation mode.

(Embodiment 6)

As illustrated in FIG. 7, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.35 Ga₀.70 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.30 Ga₀.70 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 330 angstrom

Composition: Al₀.38 Ga₀.62 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.30 Ga₀.70 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.30 Ga₀.70 As

n-type carrier block layer 3

Thickness: 330 angstrom

Composition: Al₀.38 Ga₀.62 As

FIG. 23 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 24 shows a measured result in theradiation mode.

(Embodiment 7)

As illustrated in FIG. 8, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.30 Ga₀.70 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.30 Ga₀.70 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 500 angstrom

Composition: Al₀.38 Ga₀.62 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.30 Ga₀.70 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.30 Ga₀.70 As

n-type carrier block layer 3

Thickness: 500 angstrom

Composition: Al₀.38 Ga₀.62 As

FIG. 23 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 24 shows a measured result in theradiation mode.

(Embodiment 8)

As illustrated in FIG. 9, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.30 Ga₀.70 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.30 Ga₀.70 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 50 angstrom

Composition: Al₀.50 Ga₀.50 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.30 Ga₀.70 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.30 Ga₀.70 As

n-type carrier block layer 3

Thickness: 50 angstrom

Composition: .[.Al₀.30 Ga₀.70 As.]. .Iadd.Al₀.50 Ga₀.50 As .Iaddend.

FIG. 25 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 26 shows a measured result in theradiation mode.

(Embodiment 9)

As illustrated in FIG. 10, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.30 Ga₀.70 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.30 Ga₀.70 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 330 angstrom

Composition: Al₀.50 Ga₀.50 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.30 Ga₀.70 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.30 Ga₀.70 As

n-type carrier block layer 3

Thickness: 330 angstrom

Composition: Al₀.50 Ga₀.50 As

FIG. 25 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 26 shows a measured result in theradiation mode.

(Embodiment 10)

As illustrated in FIG. 11, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.30 Ga₀.70 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.30 Ga₀.70 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 500 angstrom

Composition: Al₀.50 Ga₀.50 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.30 Ga₀.70 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.30 Ga₀.70 As

n-type carrier block layer 3

Thickness: 500 angstrom

Composition: Al₀.50 Ga₀.50 As

FIG. 25 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 26 shows a measured result in theradiation mode.

(Embodiment 11)

As illustrated in FIG. 12, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 50 angstrom

Composition: Al₀.50 Ga₀.50 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.25 Ga₀.75 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.25 Ga₀.75 As

n-type carrier block layer 3

Thickness: 50 angstrom

Composition: Al₀.50 Ga₀.50 As

FIG. 27 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 28 shows a measured result in theradiation mode.

(Embodiment 12)

As illustrated in FIG. 13, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 135 angstrom

Composition: Al₀.50 Ga₀.50 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.25 Ga₀.75 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.25 Ga₀.75 As

n-type carrier block layer 3

Thickness: 135 angstrom

Composition: Al₀.50 Ga₀.50 As

FIG. 27 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 28 shows a measured result in theradiation mode.

(Embodiment 13)

As illustrated in FIG. 14, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 200 angstrom

Composition: Al₀.50 Ga₀.50 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.25 Ga₀.75 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.25 Ga₀.75 As

n-type carrier block layer 3

Thickness: 200 angstrom

Composition: Al₀.50 Ga₀.50 As

FIG. 27 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 28 shows a measured result in theradiation mode.

(Embodiment 14)

As illustrated in FIG. 15, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 330 angstrom

Composition: Al₀.50 Ga₀.50 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.25 Ga₀.75 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.25 Ga₀.75 As

n-type carrier block layer 3

Thickness: 330 angstrom

Composition: Al₀.50 Ga₀.50 As

FIG. 27 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 28 shows a measured result in theradiation mode.

(Embodiment 15)

As illustrated in FIG. 16, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 50 angstrom

Composition: Al₀.65 Ga₀.35 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.25 Ga₀.75 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.25 Ga₀.75 As

n-type carrier block layer 3

Thickness: 50 angstrom

Composition: Al₀.65 Ga₀.35 As

FIG. 29 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 30 shows a measured result in theradiation mode.

(Embodiment 16)

As illustrated in FIG. 17, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 100 angstrom

Composition: .[.Al₀.35 Ga₀.65 As.]. .Iadd.Al₀.65 Ga₀.35 As .Iaddend.

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.25 Ga₀.75 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.25 Ga₀.75 As

n-type carrier block layer 3

Thickness: 100 angstrom

Composition: .[.Al₀.35 Ga₀.65 As.]. .Iadd.Al₀.65 Ga₀.35 As .Iaddend.

FIG. 29 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 30 shows a measured result in theradiation mode.

(Embodiment 17)

As illustrated in FIG. 18, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 200 angstrom

Composition: Al₀.65 Ga₀.35 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.25 Ga₀.75 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.25 Ga₀.75 As

n-type carrier block layer 3

Thickness: 200 angstrom

Composition: Al₀.65 Ga₀.35 As

FIG. 29 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 30 shows a measured result in theradiation mode.

(Embodiment 18)

As illustrated in FIG. 19, the n-type buffer layer 10 having a thicknessof 0.5 μm is formed on the n-type substrate 8 composed of GaAs. Formedsequentially on this layer are the n-type clad layer 1, the n-type lightwave guide layer 2, the n-type carrier block layer 3, the active layer4, the p-type carrier block layer 5, the p-type light wave guide layer 6and the p-type clad layer 7. The n-type cap layer 11 is formed as anuppermost layer thereon.

The following are concrete configurations of the respective layers.

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

p-type light wave guide layer 6

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type light wave guide layer 2

Thickness: 0.46 μm

Composition: Al₀.25 Ga₀.75 As

n-type clad layer 1

Thickness: 1.0 μm

Composition: Al₀.35 Ga₀.65 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that the4-layered quantum well layers 13 are each partitioned by the barrierlayers 14 between the side barrier layers 12 deposited on the innerwalls of the respective carrier block layers 5, 3 in the area sandwichedin between the p-type carrier block layer 5 and the n-type carrier blocklayer 3. The concrete configurations of this active layer 4 are given asfollows:

p-type carrier block layer 5

Thickness: 280 angstrom

Composition: Al₀.65 Ga₀.35 As

Side barrier layer 12

Thickness: 25 angstrom

Composition: Al₀.25 Ga₀.75 As

Quantum well layer 13

Thickness: 55 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.25 Ga₀.75 As

n-type carrier block layer 3

Thickness: 280 angstrom

Composition: Al₀.65 Ga₀.35 As

FIG. 29 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 30 shows a measured result in theradiation mode.

(Comparative Example)

FIG. 20 is a schematic plan view showing a composition of a quantum welltype laser element based on a conventional structure which ismanufactured for comparisons with the above-mentioned Embodiments 1-18.

The following are concrete configurations of the respective layers,

n-type cap layer 11

Thickness: 0.3 μm

Composition: GaAs

p-type clad layer 7

Thickness: 1.5 μm

Composition: Al₀.65 Ga₀.35 As

n-type clad layer 1

Thickness: 1.5 μm

Composition: Al₀.65 Ga₀.35 As

n-type buffer layer 10

Thickness: 0.5 μm

Composition: GaAs

n-type substrate 8

Composition (100) GaAs

The active layer 4 as shown in exploded view is formed such that4-layered quantum well layers 13 are partitioned by barrier layers 14 inan area sandwiched in between side barrier layers 12. The concreteconfigurations of this active layer 4 are given as follows:

Side barrier layer 12

Thickness: 120 angstrom

Composition: Al₀.30 Ga₀.70 As

Quantum well layer 13

Thickness: 50 angstrom

Composition: GaAs

Barrier layer 14

Thickness: 50 angstrom

Composition: Al₀.30 Ga₀.70 As

FIG. 21 illustrates a guided mode profile (near-field pattern) in thedirection vertical to the epitaxy layer with respect to the structureshown in this embodiment. FIG. 22 shows a measured result in theradiation mode.

As obvious from FIG. 21, the weakly guiding semiconductor laser exhibitsa center-pointed characteristic curve having exponential function tailson both sides. In contrast, the Embodiments 1-18 exhibit characteristicforms similar to a Gaussian beam. For this reason, using thesemiconductor laser in the present embodiment decreases the beamintensity in the active layer 4 (mode center), as shown in FIG. 21,where an optical damage is caused even with a mode expansion to the sameextent as that in the prior arts. As shown by the measured results inTable 1 which follows, a level of the catastrophic optical damage (COD)can be remarkably raised. Namely, a reduction in radiation angle and aremarkable improvement in the level of the optical damage in the presentembodiments 1-3 become more apparent than in the comparative example.Note that an emission wavelength (angstrom) of the laser isapproximately 8000 angstrom in Table 1. Further, the optical damagelevel and the slope efficiency are each optical outputs per edgesurface.

                                      TABLE 1                                     __________________________________________________________________________                         RADIATION                                                                            COD THRESHOLD                                                                            SLOFE                                               NORMALIZED                                                                            ANGLE  LEVEL                                                                             CURRENT                                                                              EFFICIENCY                             LD TYPE      FREQUENCY                                                                             Θ⊥Θ∥                                                       (mW)                                                                              (mA)   (mW/mA)                                __________________________________________________________________________    EMBODIMENT I 1.6     25°                                                                           250 90     0.5                                    STRUTURE IN FIG. 2   5°                                                EMBODIMENT 2 1.6     14°                                                                           500 300    0.5                                    STRUCTURE IN FIG. 3  4°                                                EMBODIMENT 3 3.5     18°                                                                           400 250    0.5                                    STRUCTURE IN FIG. 4  5°                                                COMPARATIVE EXAMPLE                                                                        0.28    22°                                                                           100 75     0.4                                    STRUCTURE IN FIG. 20 8°                                                __________________________________________________________________________

Industrial Applicability

In the industrial fields where the high-output semiconductor laser isemployed for communications, optical recording on optical disks or thelike, laser printers, laser medical treatments and laser machining, etc.according to the present invention, the high-efficiency semiconductorlaser exhibiting a good beam profile at the low radiation beam angle canbe obtained. Besides, it is possible to manufacture the high-outputsemiconductor laser by avoiding the concurrent optical damage of theedge surface with a simple structure. Especially in the Al_(x) Ga_(1-x)As semiconductor laser, the Al composition of the wave guide layer canbe reduced, thereby facilitating the manufacturing process.

For this reason, the element of the present invention can be utilized inthe form of the high-efficiency semiconductor laser device. Furthermore,the semiconductor laser can be used as an excitation source of asolid-state laser. The solid-state laser may involve the use of lasermediums such as Nd:YAG and Nd:YLF. If the semiconductor laser isemployed as an excitation source of the solid-state laser, the problemis a method of connecting the semiconductor laser to the laser medium.Generally, excitation beams from the semiconductor laser are focused ata high efficiency through such a lens as to mode-match an excitationvolume of the semiconductor laser with a mode volume of the laseroscillator.

In the laser element according to this invention, the beams may befocused by use of the lens as described above. As illustrated in FIGS.32 and 33, the excitation beams from a semiconductor laser element 21can be made to strike on a laser medium 23 without effecting any opticalprocessing on the excitation beams from the semiconductor laser element21. Incidentally, the numeral 24 designates an output mirror. Note thatFIG. 32 shows a direct-connection type wherein the semiconductor laserelement 21 is connected directly to the laser medium 23, while FIG. 33illustrates a fiber connection type semiconductor laser excitationsolid-state laser device in which the semiconductor laser element 21 isconnected via an optical fiber 22 to the laser medium 23.

What is claimed is:
 1. A semiconductor laser element including an activelayer having a light guiding function comprising:a pair of carrier blocklayers sandwiching said active layer, for reducing the light guidingfunction of said active layer, a pair of wave guide layers sandwichingsaid pair of carrier block layers, and a pair of clad layers sandwichingsaid pair of wave guide layers, wherein V₂ corresponding to thenormalized frequency of the wave guide layer is in the range of π/4-π,and is defined by

    V.sub.2 =(πd.sub.2 /λ)·(N.sub.0.sup.2 -N.sub.3.sup.2).sup.0.5

where π is the ratio of the circumference of a circle to its diameter,d₂ is the effective thickness between said two clad layers, λ is theoscillation wave length, N₀ is the effective refractive index of saidwave guide layer, and N₃ is the refractive index of said clad layer. 2.The semiconductor laser element according to claim 1, wherein thebandgap profile along the vertical direction of said wave guide layer isa planar or spherical oblique bandgap which becomes narrower with closerproximity to said carrier block layers from the horizontal exteriorsection.
 3. The semiconductor laser element according to claims 1 or 2,wherein V₁ relative to the normalized frequency V in a guided mode aredefined by:

    V.sub.1 =π·d.sub.1 /λ·(N.sub.0.sup.2 -N.sub.2.sup.2).sup.0.5

where π is the ratio of the circumference of a circle to its diameter,d₁ is the thickness of said carrier block layer, λ is the oscillationwavelength, N₂ is the refractive index of said carrier block layer,wherein the relationship of V₁ <V₂ /10 is established.
 4. Thesemiconductor laser element according to claim 3, wherein an energy gapdifference E (eV) between said wave guide layer and said carrier blocklayer is given by:

    E>(2.5·10.sup.3 /d.sub.1.sup.2)

where d₁ (angstrom) is the thickness of said carrier block layer.
 5. Thesemiconductor laser element according to claim 4, wherein Al_(x)Ga_(1-x) As(0≦x<1) is employed, and the composition of said wave guidelayer is:

    Al.sub.x Ga.sub.1-x As(0≦x<0.35).


6. The semiconductor layer element according to claim 4, wherein V₀ isgiven by:

    V.sub.0 =π·d.sub.0 /λ·(N.sub.1.sup.2 -N.sub.0.sup.2).sup.0.5

where d₀ is the thickness of said active layer, when said active layeris a quantum well, V₀ is defined as

    V.sub.0 =N·π·d.sub.w /λ(N.sub.1.sup.2 -N.sub.0.sup.2).sup.0.3

where d_(w) is the thickness of said quantum well layer, N₁ is therefractive index of said quantum well layer, N₀ is the refractive indexof said wave guide layer, and N is the number of said quantum wells, anda relationship of .[.(V₀ /3)<V₁ <5V₀ .]. (.Iadd.V₀ /3)<V₁ <V₀.Iaddend.is established.
 7. A laser device using said semiconductorlaser element according to any .Iadd.one .Iaddend.of claims 1.Iadd.,.Iaddend..[.or.]. 2 .Iadd.or 12..Iaddend.
 8. A semiconductor laserexcitation solid-state laser device using said semiconductor laserelement according to any .Iadd.one .Iaddend.of claims 1.Iadd.,.Iaddend..[.or.]. 2 .Iadd.or 12, .Iaddend.as a laser excitation lightsource.
 9. The semiconductor laser excitation solid-state laser deviceaccording to claim 8, wherein the excitation light outputted from saidlaser element enters a solid-state laser without employing a lens. 10.The semiconductor laser element according to claim 1, wherein therefractive index of said wave guide layer increases monotonously withapproaching carrier block layer.
 11. The semiconductor laser elementaccording to claim 5, wherein the relationship between Δx and d₁(angstrom) falls within the following range

    2.2·10.sup.3 /d.sub.1.sup.2 <Δx<5.0·10.sup.4 /d.sub.1.sup.2

where Δx is aluminum composition difference between said carrier blocklayer (x₁) and said wave guide layer (x₂); (Δx=x₁ -x₂), and d₁ is thethickness of said carrier block layer. .Iadd.
 12. A semiconductor laserelement including an active layer having a light guiding functioncomprising:a pair of carrier block layers sandwiching said active layer,for reducing the light guiding function of said active layer, a pair ofwave guide layers sandwiching said pair of carrier block layers, and apair of clad layers sandwiching said pair of wave guide layers, whereinV₁ relative to the normalized frequency V in a guided mode are definedby:

    V.sub.1 =π·d.sub.1 /λ·(N.sub.0.sup.2 -N.sub.2.sup.2)0.5

and V₂ corresponding to the normalized frequency of the waveguide layeris defined by:

    V.sub.2 =π·d.sub.2 /λ)·(N.sub.2.sup.2 -N.sub.3.sup.2).sup.0.5

where π is the ratio of the circumference of a circle to its diameter,d₁ is the thickness of said carrier block layer, λ is the oscillationwavelength, N₂ is the refractive index of said carrier block layer, d₂is the effective thickness between said two clad layers, N₀ is theeffective refractive index of said wave guide layer, and N₃ is therefractive index of said clad layer, wherein the relationship of V₁ <V₂/10 is established..Iaddend.